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https://issues.apache.org/jira/browse/HDFS-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248693#comment-13248693
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Sanjay Radia commented on HDFS-2983:
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Upgrades involves snapshots on NN and DNs. Snapshots are not just for layout
changes but also for data protection against a version change that introduced a
bug that has the potential to wipe out a portion of the data. (other systems
ask the admin to do a backup before starting the upgrade - that does not make
sense for HDFS).
HDFS's snapshot feature is a unique and powerful part of HDFS's upgrade.
Yahoo does snapshot as part of all upgrades, except for EBFs that do not
touching the core of the file system.
At this stage I don't know what snapshots mean for rolling upgrades.
This requires further thought.
> Relax the build version check to permit rolling upgrades within a release
> -------------------------------------------------------------------------
>
> Key: HDFS-2983
> URL: https://issues.apache.org/jira/browse/HDFS-2983
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.0.0
> Reporter: Eli Collins
> Assignee: Aaron T. Myers
> Attachments: HDFS-2983.patch
>
>
> Currently the version check for DN/NN communication is strict (it checks the
> exact svn revision or git hash, Storage#getBuildVersion calls
> VersionInfo#getRevision), which prevents rolling upgrades across any
> releases. Once we have the PB-base RPC in place (coming soon to branch-23)
> we'll have the necessary pieces in place to loosen this restriction, though
> perhaps it takes another 23 minor release or so before we're ready to commit
> to making the minor versions compatible.
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